The disclosure relates to a fluid-operated drive, particularly an actuating drive, such as a pneumatic or hydraulic drive, for a field device of a processing plant, such as a chemical plant, particularly petrochemical plant, a power station, a brewery or the like.
Such drives are used to communicate actuating forces to a control valve, such as a regulating or safety valve, in order to set the safety valve to a desired regulating or safety position. For this purpose, the fluidic drive chambers can be connected to a position controller, which conducts a fluidic actuating signal to the drive.
The fluid-operated drive has a basic drive, which is operated fluidically, such as pneumatically or hydraulically, with a basic working chamber, which is to be loaded fluidically, and possibly a return chamber. The basic working chamber is delimited by a basic drive housing part and by a basic actuating piston, which is guided in a fluid-tight manner in the basic drive housing part. By means of the basic drive, which can in particular be coupled to the position controller, a desired control position for the control valve can be set in the event of a corresponding fluidic loading of the basic working chamber and, possibly, the return chamber.
In addition to the fluidic basic drive, a spring-loaded safety mechanism can be provided on the drive, which forces a safety position of the control valve in the event of a corresponding pressure drop. A fluid-operated drive of this type is known from WO 2012/073172 A1, in which a pneumatic basic drive with a basic working chamber and a return chamber is separated from a supplementary drive, which is arranged in series with the basic drive. The supplementary drive has a supplementary actuating piston, which can actuate the basic actuating piston by means of a supplementary actuating rod, if a certain safety operating position is to be assumed by the control valve. The supplementary actuating piston is set by a pressure spring, which is supported on a cover of the drive housing. The actuating forces of the pressure spring for reaching the safety position are released if pneumatic pressure is output into a supplementary pneumatic supplementary working chamber. It has been shown that fluidic drives of this type with a basic drive and a supplementary drive demand a large installation space in the actuating direction and in this respect are not always suitable for use on field devices of processing plants.